I would love that. I’m not sure if that works, since afaik the law only regulates the publication of your picture and profiting off of someone’s photo. In cases of AI training you usually publish it yourself and for example Facebook and Reddit already make you agree to using your photo however they want.

I wonder if AI companies could be sued for using pictures from a private website for training.

I think that could fall under “Recht am eigenen Bild” (right to your own picture). It gives you the right to decide how images of you are used. If he profits off of photos/videos of her, she should have the right to sue him. It might also be illegal to publish the videos under GDPR law, especially in combination with more personal information like first name or city.

However, big festivals like the Oktoberfest often have a disclaimer that you agree to being filmed and your picture being published due to TV, press etc. being there. I don’t know how that would work.